Hi

Yes, you can definitely complete  syllabus of both class 11th and 12th together , there are many students who are not able to complete the syllabus of class 11th  and they still have some leftover chapters when they move on to class 12,  not only this ,they are able to complete both class XI, XII syllabus managing their time effectively, you can do the same.

What you need to do is , divide the time you have for studies into two parts ,for studying class 11 and class 12 syllabus , for example if you study eight hours a day ,then give 3 hours to class 11 syllabus and 5 hours for class 12 syllabus or you can even study 4 days class 12 syllabus and the remaining three days of week class 11 syllabus. So follow this and you will be able to complete  syllabus of both 11and 12th

Thankyou